A millimeter-wave shared-aperture transmit-reflectarray antenna for single-/dual-beam switching in V2X systems

This paper presents a millimeter-wave (mm-wave) shared-aperture transmit–reflectarray (TRA) with split-dipole excitation, targeting beam switching in vehicular communication systems. A dual-polarized transmit–reflect (TR) unit cell (UC) operating in the n258 band (24–28 GHz) is developed to support dynamic coverage and point-to-multipoint links in vehicle-to-everything (V2X) scenarios, enabling broadband and independent beam control. The transmission path employs stacked multi-resonant dipoles interconnected by metallic vias to enhance interlayer coupling and radiation efficiency, whereas the reflection path utilizes vertical dipoles with chamfered plates to achieve wideband reflective responses. Nearly parallel phase responses across the operating band facilitate broadband beamforming with consistent aperture utilization. Through orthogonal interleaving of the UCs, polarization diversity and efficient aperture reuse are realized, yielding aperture efficiencies of 19.6% (transmission) and 33.4% (reflection), with isolation exceeding 38 dB. A dual-polarized SIW-fed broadband feed ensures stable gains of 21.4 dBi and 19.9 dBi for the transmitted and reflected modes, respectively, with cross-polarization levels below - 21.7 dB. By switching between feed ports, the 15 × 15 array reconfigures between a transmitted single beam and dual reflected beams, thereby enhancing link reliability, spatial reuse, and coverage adaptability in dynamic vehicular environments. Measured results show that the transmitted single beam attains a peak gain of 21.4 dBi with a 3-dB gain bandwidth of 24.6–28 GHz, while the reflected dual beams achieve a peak gain of 19.9 dBi with a 3-dB gain bandwidth of 24–27.4 GHz.